In DE-A 42 34 290, a description is given of a pressure sensor
having a rotationally symmetrical ceramic sensor element, PA1 having a rotationally symmetrical housing exhibiting an axial bore, PA1 the diameter of which decreases in the direction of the front side, which faces the measuring medium, and PA1 having a single sealing element which is introduced between the housing and the outer surface of the pressure sensor such that it is flush with the front thereof and consists of an organic material. PA1 that the sensor element is connected in a gas-tight manner to the housing by the adapter, PA1 that the proposed method for clamping in the sensor element is stress-free, PA1 that the corrosion-resistance and the mechanical strength of the active sensor surface can be fully utilized since the fastening of the sensor element and the adapter are equally sturdy and corrosion-resistant, PA1 that such a pressure sensor can be used in potentially explosive areas, and PA1 that the pressure sensor, with the sensor element installed such that it is flush with the front thereof, can be cleaned particularly well and is thus very well suited for applications in the food industry.
A disadvantage of such a pressure sensor is that a sealing element of this type is necessary in order to fix the ceramic sensor element in the housing in a pressure-tight and stress-free manner. However, these seals are not fully gas-tight. This is because gas molecules pass by diffusion through the seal into the interior of the housing. Moreover, the corrosion-resistance of said seals is, by far, not as good as that of the ceramic sensor element.
This basic problem is not remedied in any way by high-outlay designs, as are described, for example, in EP-B 461 459. The latter specifies a pressure sensor having a ceramic sensor, that surface of the ceramic sensor against which the sealing element rests being provided with a glass layer in order to improve the sealing. Although the contact surface between the glass layer and seal is much more impermeable than between the ceramic and seal, since glass has a smoother surface than ceramic, the gas diffusion through the seal is not reduced in any way.
The safety regulations in a large number of countries require gas-tight separation of measuring medium and electronics if the pressure sensors are to be used in potentially explosive areas, e.g. with flammable gases or liquids. At present, in order to achieve this, contact pins are glazed in over a specific length or use is made of similar high-outlay lead-throughs for electric lines.
Clamping in of the sensor may also be rendered gas-tight in other ways. Diaphragm seals, such as those described, for example, in EP-A 607 482, may be provided upstream of the sensor element. On the side which faces the measuring medium, such diaphragm seals exhibit a diaphragm usually consisting of a thin corrosion-resistant metal.
Furthermore, the metal diaphragm is very thin and thus sensitive. Abrasive measuring media easily produce plastic deformation of the diaphragm and thus measuring errors.
The object of the invention is thus to specify a pressure sensor having a ceramic sensor element and a metallic housing, into which pressure sensor the sensor element is installed in a gas-tight manner.